Senator Elizabeth Warren spoke at length this week about her vision for improving the American health care system, like strengthening the Affordable Care Act and making prescription drugs more affordable. Twice, though, she ignored a question posed to her: Would she support eliminating private health insurance in favor of a single-payer system?

“Affordable health care for every American” is her goal, Ms. Warren said on Bloomberg Television, and there are “different ways we can get there.”

To put it another way: I am not walking into that political trap.

Ms. Warren of Massachusetts and three other liberal presidential candidates support a Medicare for All bill, which would create a single-payer health plan run by the government and increase federal spending by at least $2.5 trillion a year, according toseveralestimates. But Ms. Warren’s determination to sidestep an essential but deeply controversial issue at the heart of the single-payer model — would people lose the choices offered by private insurance? — illustrated one of the thorniest dilemmas for several Democrats as the 2020 primary gets underway.

Their activist base, inspired by Senator Bernie Sanders of Vermont, believes that the party should unabashedly pursue universal health care, ending private insurance entirely. But polls indicate that the broader electorate, particularly the moderate- and high-income voters who propelled the party’s sweeping suburban gains in the midterms, is uneasy about this “Medicare for all” approach in which many would lose their current insurance options and pay higher taxes.

Senator Kamala Harris of California drew immediate attacks from Republicans this week by taking on the issue that Ms. Warren dodged. Ms. Harris breezily acknowledged in a CNN town hall forum that she would “eliminate all of that,” referring to ending private insurance in a country where almost 60 percent of the population receives coverage through an employer.

Her remark triggered an intraparty debate about an issue that until now had been largely theoretical: A decade after Democrats pushed through the most significant expansion of health care since the Great Society, should they build incrementally on the Affordable Care Act or scrap the insurance sector entirely and create a European-style public program?

Four Democratic presidential candidates — Ms. Harris, Ms. Warren, Senator Kirsten Gillibrand of New York and Senator Cory Booker of New Jersey — are among the co-sponsors of Mr. Sanders’sMedicare for All bill, which would replace the Affordable Care Act with a single government health plan for all Americans. Medicare is the federal program providing health coverage to people 65 and older.

The concept of Medicare for all has become popular with Democrats: 81 percent support it, according to a recent Kaiser poll. Yet voter opposition to surrendering the insurance they are used to led to a backlash over President Barack Obama’s repeated promise that “if you like your plan, you can keep your plan” after it proved false for several million people under his health law. Many Democrats are keenly aware of that backlash, and the 2020 presidential race will be the first where many of the party’s leading candidates will have to explain and defend the meaning of Medicare for all.

For now, as Ms. Warren demonstrated, many candidates do not want to wrestle publicly with the details. After Ms. Harris’s comment, her aides hastened to add that she would also support less sweeping changes to health care; like most other candidates, Ms. Harris declined an interview request. And by Friday, Mr. Booker, hours after announcing his presidential bid, sought to curtail the matter by offering a brisk “no” when asked if he supported eliminating private coverage.

Yet there is one likely 2020 contender who is thrilled to discuss Medicare for all.

Mr. Sanders, in an interview, did not mince words: The only role for private insurance in the system he envisioned would be “cosmetic surgery, you want to get your nose fixed.”

“Every candidate will make his or her own decisions,” Mr. Sanders said, but “if I look at polling and 70 percent of the people support Medicare for All, if a very significant percentage of people think the rich, the very rich, should start paying their fair share of taxes, I think I’d be pretty dumb not to develop policies that capture what the American people want.”

But Michael R. Bloomberg, the former New York City mayor who is considering a 2020 bid on a centrist Democratic platform, said it would be folly to even consider a single-payer system. “To replace the entire private system where companies provide health care for their employees would bankrupt us for a very long time,” Mr. Bloomberg told reporters in New Hampshire on Tuesday.

The Congressional Budget Office has not scored Mr. Sanders’s Medicare for All bill, but a study last year by the Mercatus Center of George Mason University predicted it would increase federal spending by at least $32.6 trillion over the first decade. The cost could be even greater, the study says, if the bill overestimated the projected savings on administrative and drug costs, as well as payments to health care providers.

The divide between Mr. Sanders, a democratic socialist, and Mr. Bloomberg, a Republican-turned-independent-turned-Democrat, reflects the large chasm in a party that has been reshaped by President Trump.

The president’s hard-line nationalism has simultaneously nudged Democrats to the left, emboldening them to pursue unambiguously liberal policies, and drawn independents and moderate Republicans to the party because they cannot abide his incendiary conduct and demagogy on race. These dueling forces have created a growing but ungainly coalition that shares contempt for Mr. Trump but is less unified on policy matters like health care.

And these divisions extend to what is wisest politically.

Liberals argue that the only way to drive up turnout among unlikely voters or win back some of the voters uneasy with Hillary Clinton’s ties to corporate interests is to pursue a bold agenda and elevate issues like Medicare for all.

“Those who run on incremental changes are not the ones who are going to get people excited and get people to turn out,” said Representative Pramila Jayapal of Washington, the co-chair of the Congressional Progressive Caucus.

And by preserving their options, Democrats risk alienating liberal primary voters, some of whom consider support for Medicare for all a litmus test.

“The center is not a good place to be on these policies anymore,” said Mary O’Connor, 61, a substitute teacher and horse farmer in Middleburg, Va., who wants a single-payer system. “I’ll be watching extremely closely, and I will most likely jump on board and volunteer for whoever it is that’s going to be the most forceful for this.”

But moderates believe that most Democratic primary voters are more fixated on defeating Mr. Trump than applying litmus tests — and that terminating employer-sponsored insurance would only frighten the sort of general election voters who are eager to cast out Mr. Trump but do not want to wholly remake the country’s health care system.

“Most of the freshmen who helped take back the House got elected on: ‘We’re going to protect your health insurance even if you have a pre-existing condition,’ not ‘We’re going to take this whole system and throw it out the window,’” said Kenneth Baer, a Democratic strategist.

While polling does show that Medicare for all — a buzz phrase that has lately been applied to everything from single-payer health care to programs that would allow some or all Americans to buy into Medicare or Medicaid — has broad public support, attitudes swing significantly depending on not just the details, but respondents’ age and income.

On the House side, a bill similar in scope to Mr. Sanders’s is under revision and will soon be reintroduced with Ms. Jayapal as the main sponsor. Other Democrats have introduced less expansive “Medicare buy-in” bills, which would preserve the current system but would give certain Americans under 65 the option of paying for Medicare or a new “public option” plan. Another bill would give every state the option of letting residents buy into Medicaid, the government health program for poor Americans.

The buy-in programs would generally cover between 60 and 80 percent of people’s medical costs and would require much less federal spending because enrollees would still pay premiums and not everyone would be eligible. Some proponents, like Senator Jeff Merkley, Democrat of Oregon, have described them as a steppingstone on the way to a full single-payer system; some of the Democrats running for president are co-sponsoring these “Medicare for more” bills as well as Mr. Sanders’s.

Mr. Sanders has suggested options to raise the money needed for his plan, such as a new 7.5 percent payroll tax and a wealth tax on the top 0.1 percent of earners. He has also predicted several trillion dollars in savings over 10 years from eliminating the tax exclusion that employers get on what they pay toward their workers’ insurance premiums, and other tax breaks.

But Robert Blendon, a health policy professor at Harvard who studies public opinion, said it would be wise not to delve into financing details for now.

“The reason it failed in Vermont and Colorado was taxes,” Professor Blendon said, referring to recent efforts to move to a near-universal health care system in those states, which flopped resoundingly because they would have required major tax increases. “But Democratic primary voters will not go deep into asking how these plans will work. What they will say is, ‘Show me you have a principle that health care is a human right.’”

The general election will be a different story, Professor Blendon added. If Ms. Harris were to become the Democratic nominee and keep embracing the idea of ending private coverage, he argued, “she’s going to have terrible problems.”

The difficulty for Democrats, added Ezekiel Emanuel, a former Obama health care adviser, is that many voters look at the health care system the same way they view politics. “They say Congress is terrible but I like my congressman,” as Mr. Emanuel put it.

According to the Gallup poll, 70 percent of Americans with private insurance rate their coverage as “excellent” or “good;” 85 percent say the same about the medical care they receive. The Kaiser poll found that the percentage of Americans who support a national health plan drops by 19 percentage points when people hear that it would eliminate insurance companies or that it would require Americans to pay more in taxes.

Among those who make over $90,000 a year — the sort of voters in the House districts that several Democrats captured in the midterms — those surveyed in the Kaiser poll were particularly wary of an all-government system: 64 percent in this income group said they would oppose a Medicare for all plan that terminated private insurance.

In Vermont, where former Gov. Peter Shumlin shelved his ambitious plan for a single-payer system in 2014 after conceding it would require “enormous” new taxes, advocates for universal health care are now resigned to a more incremental approach.

Dr. Deb Richter, a primary care doctor who helped lead the state’s single-payer movement, said that while the Democratic field is “going to have to face the T word,” being upfront about the required tax increases, she now thinks phasing in a government-run system is a better approach.

“There’s ways of doing this that don’t have to happen all at once,” she said, pointing to a push in Vermont to start with universal government coverage for primary care only. “But you need to talk about the end goal: We are aiming for Medicare for all, and this is a way of getting it done.”

PASSING UNIVERSAL HEALTH CARE WITHOUT A SYSTEM OF PAYING FOR IT WOULD INVITE SCORN FROM THE MEDIA AND THE PUBLIC. BUT PASSING IT WITH IMMENSE NEW TAXES WOULD PUT DEMOCRATS IN POLITICAL JEOPARDY.

Assembly Speaker Anthony Rendon applied brakes to Senate Bill 562 in June, saying it “was sent to the Assembly woefully incomplete and has “potentially fatal flaws…including the fact it does not address many serious issues, such as financing, delivery of care (and) cost controls.”

That stance generated a torrent of personal invective from the measure’s advocates in the Democratic Party’s left – or Berniecrat – wing, driven by the California Nurses Association.

There’s a similar divide among the Democratic candidates for governor, with Lt. Gov. Gavin Newsom the most insistent advocate of expanding coverage.

Like Rendon, Newsom’s chief rivals, former Los Angeles Mayor Antonio Villaraigosa and Treasurer John Chiang, endorse universal health care in principle, but are leery about how it would be financed.

A Senate Appropriations Committee analysis pegs costs of universal coverage at $400 billion a year, but suggests that half could be covered by redirection of existing federal, state and local government health care spending.

It added that “about $200 billion in additional taxes would be needed to pay for the remainder,” but also noted that half or more of that burden could be offset by eliminating direct health care costs now borne by consumers and their employers.

To put that in perspective, even $100 billion in new taxes would be the equivalent of a one-third increase in the $300 billion a year now levied by state and local governments.

In theory – one advanced by advocates – the two-thirds “supermajorities” in the Legislature and the governor could levy new taxes of that magnitude.

In practice, however, even if the supermajorities survive the recent spate of sexual harassment resignations and next year’s elections, there’s virtually no chance of such a vote.

Rendon knows that passing universal health care without a system of paying for it would invite scorn from the media and the public, but passing it with immense new taxes would put some of his Democratic members in political jeopardy.

If, however, Democrats are serious about having universal health care insurance there’s another, perhaps easier, way to do it.

That means that there are about 2.7 million Californians still lacking some form of medical coverage, although many, if not most, receive rudimentary, albeit uncompensated, care in charity clinics and hospital emergency rooms.

As many as half of them would be eligible for government-paid or -subsidized care, and covering them is potentially doable under existing programs, according to Covered California, the state’s Obamacare implementation agency.

The remainder, mostly, are maybe a million-plus undocumented immigrant adults who are, by law, ineligible.

It’s not necessary for the state to seize control of California’s entire medical care system if the real bottom line goal is covering those undocumented immigrants. It could be done for about $10 billion a year, which is a lot less than $100 billion.

However, advocates would have to publicly acknowledge that covering them is what this conflict is all about and take whatever political heat it generates.

It’s a test of whether universal coverage is a real goal, or merely political symbolism.

With the turmoil and chaos caused by the ceaseless efforts of Congress and the Trump administration to shred the Affordable Care Act, shouldn’t our legislators show more urgency to provide health security for Californians?

On Monday, an Assembly select committee will hold its first hearing “to determine the best and quickest path forward toward universal health care,” in the words of Assembly Speaker Anthony Rendon.

However, the committee has no authority to act on legislation. It is essentially a discussion group designed to give the appearance of moving forward on reform, rather than act on an existing bill, Senate Bill 562, which would guarantee health care for all Californians without huge out-of pocket costs hurting so many.

A legislative study has already concluded that a Medicare for all/single-payer approach, as SB 562 advances, is superior to all other models of health care financing.

Further, a study released in June documented the bill’s additional cost to the state budget is closer to $100 billion, not the misleading $400 billion cited by opponents. The study also offered financing proposals under which nearly all families and businesses would pay less for health care than they do now.

It is also troubling that select committee co-chairmen Jim Wood, a Healdsburg Democrat, and Joaquin Arambula, a Fresno Democrat, are the two of the three largest Assembly recipients of campaign contributions from the health care and insurance industries.

Unlike the powerless committee, SB 562 has the enormous advantage of having already passed the state Senate in June. The Assembly can take it up immediately early next year with any amendments members want to propose.

Further delays leave Californians at the mercy of the Trump administration. Consider the latest executive orders to encourage the sale of insurance plans that evade the extensive protections established by California legislators, and to cancel subsidy payments to insurers to sabotage the ACA marketplaces.

Premiums in California for “silver” plans, by far the most common under Covered California, are going up by 25 percent on average. Anthem Blue Cross rates are jumping by 37 percent, and it is pulling out of about half of California counties.

The specific impact on individuals and families varies depending on where you live, your income, how much coverage you want, and who your current insurer is. Or you may need to shop around for a non-silver plan – all with differing levels of coverage, deductibles and co-pays and that may or may not include your doctor, hospital, or other providers in its network.

Or Congress may or may not pass supplemental legislation to reverse Trump’s orders, which he may or may not support, with its own set of uncertain impacts. Everyone clear?

There’s a fix that would end Californians’ anxiety over their health coverage and cost, and establish protection for all. The people are ready. Earlier this month, nearly 1,000 activists attended 100 events in all 80 Assembly districts to talk to their neighbors about SB 562, and 10,000 people signed petitions urging its approval.

Concord resident Emily Chandler was among them. She told us she pays $800 a month for insurance but sometimes avoids going to the hospital because she can’t afford the co-pays and deductibles. She is one of 15 million Californians who, even under the ACA, are without coverage or who don’t get the care they need due to rising costs.

Californians don’t need a committee that can do little more than talk. They need real relief, SB 562.

The two leading Democrats for California governor on Sunday split over how to achieve universal health care, with Lt. Gov. Gavin Newsom defending his support for a government-run, single-payer system and former Los Angeles Mayor Antonio Villaraigosa dismissing as “pie in the sky” plans that don’t include viable financing methods.

At a union-sponsored health care forum, Villaraigosa credited the Assembly speaker for sidetracking a universal health bill, Senate Bill 562, in Sacramento, because it didn’t include a funding mechanism. He supports the concept, but argued the state’s immediate focus should be on protecting the 5 million people who could lose their coverage if Republicans and President Donald Trump succeed in repealing Obamacare.

“As governor, you gotta make the tough choices, you can’t just say ‘I want pie in the sky,’ because that doesn’t put food on people’s tables,” he said, advocating for a public option that allows people to buy into the existing Medi-Cal program.

“What I’ll never do is sell you snake oil,” added Villaraigosa. “The fact of the matter is we don’t have a plan yet.”

Newsom, a proponent of advancing the bill, cast the issue as one of leadership and commitment. He contended there is considerable “mythology” about the $400 billion annual price tag of enacting the system because the state currently spends about $368 billion a year on health care in California, nearly two-thirds of it borne by taxpayers.

“A single-payer system drives down the cost of health care; drives down the cost of prescription drugs through economies of scale; and provides more effective, efficient and universal access for those that are uninsured,” Newsom said, pointing to double-digit increases in Obamacare here. He said the financing will be worked out as the legislative process moves forward.

“It’s a question of leadership,” he added. “This is what they said about Social Security and Medicare: ‘You can’t do it …’ I’m not going to wait around for the debate to unfold in Washington, D.C. Sure, I support Medicare for all, but you got to shape the debate in California.”

The exchange between Newsom and Villaraigosa came at the forum hosted by the National Union of Healthcare Workers, which also included Democrats Delaine Eastin, a former state school’s chief, and Treasurer John Chiang.

Chiang largely sidestepped the debate over universal care, offering that the state should take an incremental approach to health care. He wants to see more “effectiveness and efficiency” in the current system.

“We have to figure out how to scale-up, the time frame we’re going to scale-up,” he said, adding, “We don’t have to go all in to provide all the services all at once. Let’s make sure that what we are implementing we can scale-up appropriately.”

Eastin, like Newsom, believes single-payer would cost “slightly more” now but far less in the long run.

“The fact of the matter is people are dying in California because we do not have affordable health care coverage for everybody,” she said, calling the solution “realistic,” and saying it could be paid for with a gross receipts tax and a partial income tax increase.

She added: “There’s nothing California can’t do if we put our minds to it.”

The single-payer measure, driven largely by the California Nurses Association, has divided Democrats and is emerging as a litmus test for 2018. Newsom, endorsed by the nurses’ union, has never trailed in public polls and fundraising, while Villaraigosa has been the second-place Democrat.

The Republicans in the race, John Cox and Travis Allen, did not attend the forum, though the host National Union of Healthcare Workers, representing 14,000 workers in California, said they were invited. After Sunday’s forum, the union voted to endorse Newsom. Eastin was runner-up.

As the nation’s Republican leaders huddle to reconsider their plans to “repeal and replace” the nation’s health law, advocates for universal health coverage press on in California, armed with renewed political will and a new set of proposals.

Organized labor and two lawmakers are leading the charge for a single, government-financed program for everyone in the state. Another legislator wants to create a commission that would weigh the best options for a system to cover everyone. And Democratic Lt. Gov. Gavin Newsom, who hopes to become the next governor, has suggested building on employer-based health care to plug holes in existing coverage.

The proposals are fueled both by a fear of losing gains under the Affordable Care Act and a sense that the law doesn’t go far enough toward covering everyone and cutting costs.

But heath policy experts say that creating any type of universal health plan would face enormous political and fiscal challenges — and that if it happens at all, it could take years.

“There are different ways to get there,” says Jonathan Oberlander, professor of social medicine and health policy at the University of North Carolina. “None of them is easy.”

The most specific California proposal comes from state Sens. Ricardo Lara (D-Bell Gardens) and Toni Atkins (D-San Diego), co-authors of legislation that would take steps toward creating one publicly financed “single-payer” program.

The bill, co-sponsored by the California Nurses Association, would aim for something like a system of “Medicare for all” in which the government, not insurers, provides payments and sets coverage rules.

Lara said the approach would get California closer to a system “that covers more and costs less.”

The bill’s authors haven’t announced how the program would be funded. And that’s where the biggest obstacle lies, said Oberlander: It would largely uproot California’s present system, in which roughly half of coverage is sponsored by employers.

If “you’re going to take health insurance largely out of the market, you’re going to disconnect it from employers,” he said. “Then you have to make up all the financing that you’re going to lose.”

There’s no way to make up for those lost employer contributions other than to introduce “very visible taxes,” Oberlander said. And that’s not the only reason why a single payer plan would be controversial. “A lot of people are satisfied with what they have,” he said.